1. Field of the Invention
The present invention generally relates to a battery control system for electric automobiles, and particularly, to a battery control system for controlling a battery of an electric automobile to cope with a significant generation of hydrogen from the battery that may occur upon a charge or discharge of the battery or with a deterioration of the battery.
2. Description of Relevant Art
In the electric automobile, a battery for a strong current service is charged from a charger and, after the charge, supplies a voltage to a motor as a load, conducting a discharge current to rotate the motor so that the automobile can travel. As the automobile travels, a remaining capacity of the battery decreases and, in due course, goes below a predetermined value for a battery controller to give an alarm for prevention of an over-discharge, while controlling the charger to re-charge the battery.
The electric automobile may run down a decline, where an acceleration pedal may be released, then the motor works as a generator that provides a restoration current. The battery is charged with the restoration current, and the battery controller controls a voltage across the battery to avoid an over-charge.
The battery for strong current service may be a lead cell or a nickel hydrogen cell, and has a tendency to generate hydrogen when brought into an over-charge or over-discharge condition. Generated hydrogen may have an undesirable concentration, as it ascends and may be accumulated under a top of an associated enclosure that may communicate with a passenger room of the automobile, in which air may become hydrogen-rich to an undesirable degree.
To avoid such a hydrogen-rich state, Japanese Patent Application Laid-Open Publication No. 8-186901 has disclosed a conventional system which checks a battery voltage to detect an over-charge state and an over-discharge state, and responds to a thus detected state to drive a fan for ventilation of an automobile.
However, the battery has a long life and experiences repeated charge-to-discharge cycles. The battery ages and may deteriorate with an increased frequency of charge-to-discharge cycle, with a probable tendency to generate hydrogen when the battery is charged or discharges in an ordinary manner free of over-charge or over-discharge. In the conventional system, as the fan is driven in response to a detected overcharge or over-discharge, the automobile may have an increasing amount of hydrogen stagnant therein.
The battery may enter an abnormal state with an increasing or continued tendency to generate hydrogen, or may suffer from an irregular command of charge and/or discharge control with which the battery may generate a great amount of hydrogen, and a driver may want to be informed of a sign of such abnormality, so that he or she can take adequate measures.